Physical Properties of Purified Human Respiratory Mucus Glycoproteins: Effects of Sodium Chloride Concentration on the Aggregation Properties and Shape

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Abstract
The biophysical properties of purified native (nonreduced) mucus glycoproteins (mucins) isolated from lung mucus secretions of cystic fibrosis (CF) patients and subjects with normal lungs were studied using the technique of light scattering. The effects of different NaCl concentrations and 6 M guanidine hydrochloride on the molecular size of mucins, their ability to form aggregates, and their shape were investigated. Under the concentration range studied (0.05—3.5 mg/ml), in buffered 0.03 and 0.01 M NaCl, the CF mucins had higher molecular weights (12.2 X 106 to 17.1 X 106 and 9.5 X 106 to 10.4 X 106, respectively) than those observed in buffered 0.15 M NaCl (4.3 X 106 to 6.6 X 106). These results were interpreted in terms of CF mucins self-aggregating in buffered 0.03 and 0.01 M NaCl. In contrast, in both buffered 0.3 and 0.15 M NaCl, the normal respiratory mucins had molecular weights of 6.3 X 106 to 8.6 X 106, thus suggesting the absence of normal mucin aggregation in buffered 0.03 M NaCl. In the presence of 6 M guanidine HCl both CF and normal mucins had molecular weights of about 5 X 106 and showed more extended structure (i.e., larger radius of gyration) than in the presence of 0.03 or 0.15 M NaCl. Studies of the relationship of the light scattering intensity with scattering angle showed that, under the above experimental conditions studied, both CF and normal respiratory mucins were polydisperse flexible coil-shaped molecules. The increased aggregation of CF mucins observed at lower salt concentrations may alter the viscoelastic properties of CF lung mucus secretions.